1) Technical Field of the Invention
The present invention relates to a semiconductor device, and in particular, relates to the semiconductor device facilitating electrical connection between a control circuit and a semiconductor chip incorporated in the semiconductor device.
2) Description of Related Arts
So far, the semiconductor devices have been utilized in various technical fields. Among them, a power module for supplying a large amount of controlled current to a high power motor attracts intense attention as a key device, for example, from heavy electric machinery industries and automobile industries.
Although not shown herein, the power module includes, in general, a case and an insulating substrate provided within the case. Mounted on the insulating substrate is a power semiconductor chip such as an insulating gate bipolar transistor chip and a free wheel diode chip (which are referred to simply as an “IGBT” chip and a “FWD” chip, respectively). Also, the power module includes a control board having a control circuit for providing a control signal (control current) with the power semiconductor chip, and a plurality of lead frames for leading the controlled current output from the power semiconductor chip in response to the control signals, to an external load such as a motor.
According to the conventional power module, the control board is, in general, a printed-wiring board made of material such as epoxy resin, which is stiff and has a plate-like configuration. The printed-wiring board has at least one control circuit and a plurality of terminal pads electrically connected with the gate electrodes on the IGBT chips via a plurality of conductive wires (metal thin lines). Therefore, the gate signals are supplied from the control circuit to the gate electrode of the IGBT chips, which in turn perform a switching operation in response to the gate signals.
Also, the conventional power module often includes the FWD chip reversely connected with the IGBT chip in parallel, in which an anode electrode of the FWD chip and an emitter electrode of the IGBT chip are electrically connected with the lead frames also via a plurality of the conductive wires. Thus, if four of the conductive wires are used for electrically connecting the emitter electrodes of the IGBT chip and the anode electrodes of the FWD chip with the lead frame, and also four of the conductive wires are used for electrically connecting control electrodes (such as the gate electrode, a current-sensing electrode, and a temperature-sensing electrode) of the IGBT chip with the terminal pads of the control board, eight of the conductive wires are required in total. Also, if the power module has six pairs (three pairs of phase legs, i.e., U-, V-, and W-phases legs) of the IGBT chips and the FWD chips, at least forty-eight of conductive wires are required for achieving the electrical connection to assemble the power module.
Meanwhile, such many conductive wires made by the conventional ultrasonic wire-bonding process require too much time, which costs more and thus prevents the power module from being manufactured at a reasonable cost.
To address this drawback, several techniques have been proposed for facilitating electrical connection between terminal pads. For example, one of the conventional techniques, JPA 2004-111619, discloses a power module in FIG. 1-3, which includes an insulating substrate 4, a second resin circuit board 8 with copper patterns 8b mounted on the insulating substrate 4, a heat sink 3 also provided on the insulating substrate 4, a semiconductor chip (IGBT chip) 1 mounted on the heat sink 3, and a first resin circuit board 5 with copper patterns 5b fixed on the copper patterns 8b of the second resin circuit board 8 by means of solder, in which the chip electrode of the semiconductor chip 1 is electrically connected with the copper pattern 5b of the first resin circuit board 5 via a solder ball and a solder layer. Thus, the first resin circuit board 5 has terminals at both ends connected on the copper patterns 8b of the second resin circuit board 8 and a pair of terminals at the center connected on the chip electrodes (i.e., the gate electrode and the emitter electrode) of the IGBT chip 1.
However, when the first resin circuit board 5 is assembled for connecting the pair of the terminals thereof with the gate and emitter electrodes on the IGBT chip 1 that are closely arranged, both of the terminals and electrodes have to be precisely aligned to each other. Otherwise the gate terminal (or emitter terminal) of the circuit board 5 may bridge (make a short circuit between) the gate and emitter electrodes of the IGBT chip 1. Meantime, the first resin circuit board 5 has a basic substrate made of flexible resin, which is susceptible to ambient temperature. Thus, high temperature while soldering for electrical connection between the terminals of the circuit board 5 and the chip electrodes of the IGBT chip 1 may cause difficulty to align the circuit board 5 to the IGBT chip 1. In other words, misalignment of the circuit board 5 to the IGBT chip 1 may cause connection failure of the short circuit to reduce production yield, on the other hand, precise alignment requires an worker's special caution, which increases assembling time and manufacturing cost.
Further, the copper pattern 5b on the flexible circuit board 5 is a conductive thin layer, of which wiring resistance has a lower limit to be achieved. Therefore, if a large amount of current run between the emitter electrode and the collector electrode of the semiconductor chip as the IGBT chip 1, the copper pattern 5b may be overheated and the flexible circuit board 5 may soften and melt during the switching operation, thereby inhibiting sufficient reliability of the power module during operation.